Tight gas formations, such as Khuff carbonate, pre-Khuff sandstone and shale gas formations with high compressive strength require hydraulic fracturing procedures in order to open the reservoir formation and enhance the flow of gas to the well bore for production. In such tight gas-containing reservoir formations, a perforating gun is used to initiate formation breakdown by detonating high-performance deep-penetrating shaped charges that maximize perforation length and entry hole size to start the hydraulic fracturing or “hydrofracking”, in order to enhance hydrocarbon production and optimize well flow.
The tubing-conveyed perforating (TCP) gun employs a drilling rig at the surface in operation to handle the tubing that conveys the gun to the desired depth in the well bore.
Perforating guns are available in various configurations. In each case, the key objective of the selection of the gun and the size, nature and set up of the shaped charges is to create a predetermined pattern of perforations over a predetermined wellbore interval.
The creation of deep perforations with large diameters has been addressed with varying degrees of success. To create deep perforations that bypass damaged zones, the perforation diameter should be small and the force of the shaped charge narrowly focused.
A method and apparatus are disclosed in U.S. Ser. No. 14/959,942 (US 2016/0108708) for multiple same location firings of a perforating gun to extend the depth of the initial lateral penetrations further into the surrounding formation. A latching tool and tubing-conveyed perforating (TCP) gun are lowered into the wellbore by a surface rig and engage a latch coupling that was previously secured to a section of a well casing proximate the predetermined interval in the wellbore that is to be penetrated to provide a fixed reference point. Withdrawal after the first firing and recharging of the gun, followed by its return and engagement of the latching tool with the latch coupling permits the perforation of the formation repeatedly and at the same position. The prepositioned latch coupling and releasably secured engagement of the latching tool provide a consistent, reproducible reference point at the predetermined depth and orientation for repeated use of the TCP gun in vertical and lateral wells.
An advance in the art is disclosed in published application US 2016/0160620 where the latch coupling is secured to the end of the production tubing which permits the assembly to be deployed downhole without the use of a surface rig, thereby reducing the overall costs associated with the penetration operation. The end of the tubing with the latch coupling, which serves as the gun anchoring point, are landed so that the latch coupling is proximate the perforation interval. However, if the perforation plan for the well is changed so that a perforation is to be performed at a lower depth, or further into a lateral/horizontal open hole wellbore, the accuracy at the new depth of a perforation at the same point will be jeopardized.
Current perforation practices can fail to provide a deep and large diameter penetration when the target zone is behind more than one casing. A problem also exists in formations with high compressive strength and can also fail to bypass formation damage caused by the explosive forces.
A problem to be solved then is to provide apparatus, systems and methods in preparation for hydraulic fracturing operations that operate without a rig for securely positioning a perforating gun at the desired location for the first of a planned series of firings and returning the gun after reloading at the surface to the same position and radial orientation for one or more firings to complete a plurality of reservoir perforations or penetrations to the same position in order to produce a deep penetration having a larger diameter than is currently possible.
The problem can also be stated as how to position and to subsequently return the perforating gun to the same location for successive or repeated reservoir penetration shots in wells, preferably operating without the use of a rig, i.e., perforating guns that are deployed by wireline and/or a coiled tubing unit, and also withdrawing all of the components after the penetration has been completed.
An additional problem to be addressed is maintaining the accuracy of the perforation when the perforation plan includes at least an additional perforation interval at a position in the wellbore that is displaced, e.g., beyond, the first perforation interval.
As used herein, the term “downhole” refers to both vertical and lateral wellbores. The figures illustrate vertical well orientations for convenience, and it will be understood that references to “above” and “below” are relative to the apparatus regardless of the orientation of the wellbore.
For convenience, the following describes the installation and use in a well lined with a casing, but as will be understood by one of ordinary skill in the art, the method is equally applicable to perforating an interval in an open hole wellbore.